1. Field of the Invention
This invention relates to a fluid transmission conduit assembly for use in a subterranean well to isolate fluid flow passing therethrough.
2. Description of the Prior Art
In order to recover oil in production zones after economical primary production operations have terminated, produced salt water from other zones or reservoirs is injected into the production zone by means of injection wells to cause migration of the remaining oil to the producing well. The salt water generally employed often contains a high solid content and often because of exposure to air at the well surface, the water will also contain a high concentration of dissolved oxygen. The combination of dissolved oxygen in salt water being utilized as a liquid injection medium results in a highly corrosive environment for the tubing used in the producing well. The tubing is not only subjected to this highly corrosive injection medium but it also is subjected to high pressures maintained to increase the initial and normal pressure of the production zone in the vicinity of the injection well bore.
Quite often the increased production zone pressures will cause the injected fluid to back flow through the upper end of the tubing at the top of the well as the tubing is being retrieved. If precautions are not taken, the back flow will result in need for auxiliary disposal means and procedures to avoid potential environmental damage. Typically back flow problems have been avoided by seating a wireline blanking plug into the bore of an on/off sealing connector. The plug prevents flow of fluid in either direction so that the tubing string may be pulled out of the well bore and rerun without back flow of the injected salt water. Such a procedure in not entirely satisfactory because it must be assumed that the tubing string has suffered considerable chemical deterioration resulting from oxygen corrosion and scale deposits such that the time consuming and costly running and sealing engagement of a plug by wireline cannot be reliably accomplished. Alternatively, a weighted fluid may be injected into and circulated through the tubing casing annulus into the well bore above the packer to balance the reservior pressure and thus prevent salt water back flow. This procedure is quite costly, is time consuming, and can lead to additional problems when the weighted fluid is removed from the well. Similar problems may be encountered in salt water disposal operations. Additionally the need to remove tubing strings is encountered in artificial lift wells in which gas lift mandrels must be relocated. If the well is capable of flowing at a reduced rate without artificial lift applications, a means for isolating the flow of fluid through the tubing string must be utilized.
Downhole shutoff valves which may be used with an on/off sealing connector and with a packer apparatus anchoring the tubing string to the oil well casing have been employed in the prior art to deal with these problems. The present invention encompasses the use of an improved downhole shutoff valve with an on/off tubing connector and packing apparatus to provide an assembly permitting the operator to isolate portions of the tubing string by rotary manipulation of the tubing string at the surface of the well. The packer apparatus employed with this assembly normally is designed to selectively latch and sealingly receive the bottom exterior end of the tubing string. The packer apparatus provides sealing engagement along the I.D. of the casing within the tubing casing annulus above the injection zone to completely isolate the annular area thereabove from the injection fluids. The packer apparatus can be set to anchor the tubing string with respect to the oil well casing in various ways, including rotation of the tubing string to anchor the tubing string against rotation in the opposite direction. A downhole shutoff valve can then be inserted in the tubing string at any point above the packer apparatus where flow needs to be stopped. An on/off tubing connector attached immediately above the downhole shutoff valve then permits the withdrawal of the tubing string above the downhole shutoff valve. In this invention, the downhole shutoff valve can be moved from the open to the closed position by rotation of the tubing string in a direction opposite from the initial setting direction of the packer apparatus. The tubing string above the downhole shutoff valve may be retrieved by continued rotation of the tubing string in the direction resulting in closure of the downhole shutoff valve. Such continued rotation will cause disengagement of the on/off connector and the tubing string extending thereabove. Rotation of the tubing string to initially close or open the downhole shutoff valve and subsequently disengage the on/off connector is facilitated by the use of sealing elements in this downhole shutoff valve which provides sealing integrity both from above and below the valve. This assembly can therefore be used when excess pressure exist in the tubing either above or below the valve. The downhole shutoff valve also employs valve activation means which permit a valve to be opened even in the presence of a large pressure differential which might otherwise cause the valve to stick.